When? The author appears to define her own Array type as well:
scala> class Array
defined class Array
scala> class WrappedArray(xs: Array) extends Seq // a Seq adapter for Arrays
defined class WrappedArray
scala> implicit def array2seq(xs: Array): Seq = new WrappedArray(xs)
array2seq: (xs: Array)WrappedArray
scala> new Array().ident
<console>:13: error: value ident is not a member of Array
new Array().ident
Arrays are not sequences, in either the standard Scala library or his condensation of it. The goal is still to define a single extension method for two unrelated types.
Well, sorta; the Array -> WrappedArray conversion relates them. The intent is to let you use Seq methods on Arrays, and that part works. But you don't also get RichSeq methods, even though you can use them on Seqs. I'm sure that seems obvious to you, but do you see how the author's intent is misaligned with the result?
I think that's the key takeaway: implicits aren't really a way of extending a library type, they just have some of the same effects. You still have to care about the distinction between the original type and the enhanced one, and that's, well, complex.
I agree. Implicits don't compose transitively (and for good reason), and that makes them complex. That's why I suggested to think about putting implicit conversions behind a compiler switch. They are extremely useful for what they are but not a panacea.
